Annular beam flood gun for storage tubes



Nov. 7, 1967 B. GRCNLUND 3,351,795

ANNULAR BEAM FLOOD GUN FOR STORAGE TUBES Filed March 2 9, 1966 66, Fig. 3.

Bent Gronlund,

INVENTOR.

ATTORNEY.

United States Patent 3,351,795 ANNULAR BEAM FLOOD GUN FOR STORAGE TUBES Bent Gronlund, Vista, Calif., assignor to Hughes Aircraft Qompany, Culver City, Calif. Filed Mar. 29, 1966, Ser. No. 538,318 Claims. (Cl. 313-85) The invention relates to an electron-emitting device adapted to produce a beam of high density low energy electrons and has particular utility when employed in that type of device known as a flood gun.

The field of application of the disclosed invention relates generally to cathode ray tubes and particularly that type of cathode ray tube known as a storage tube. The primary function of storage tubes is to provide a bright and persistent display of known recurring pictorial information. Accordingly, the tubes are usually of the direct view type.

In current practice there are several types of direct view storage tubes and the disclosed invention is not, per se, limited to any specific construction. Of the existent direct view tubes, the external and internal structure generally are similar. A typical structure is herein disclosed. Essentially, a storage tube consists of four elements, namely, a storage target, an adjacent phosphor viewing screen, a flood gun and a writing gun. The storage target typically consists of a fine metallic mesh screen with many hundreds of holes per linear inch. Placed on a surface of the screen is a thin layer of insulating dielectric usually on the side of the mesh facing the flood gun. The flood gun functionally covers the entire storage surface with a uniform broad beam of relatively slow moving electrons. In operation, the storage target is brought to a base potential and a charge pattern corresponding to the picture to be viewed is deposited on the surface of dielectric by the writing gun. This is accomplished as a result of the phenomenon known as secondary electron emission, namely, when the storage dielectric is struck by an electron beam having a velocity above the first crossover point the dielectric emits more electrons than it receives and, accordingly, a variable charge pattern is placed thereon, The charge pattern reflects the modulation of the writing electron beam responsive to input signals. After charge pattern disposition, each elemental area of the charge dielectric controls the transmission through the target of electrons from the flood gun in the classic manner. In areas where the charge pattern is relatively more positive, flood electrons tend to penetrate the storage mesh, and, on the other hand, in areas where the charge pattern is relatively negative, the flood electrons are repelled and do not penetrate the target. Electrons which pass through the storage target are velocity accelerated and strike the phosphor viewing screen with a relatively high energy, inducing luminescence and producing a light pattern thereon. The light pattern corresponds to the charge pattern on the dielectric storage surface. As long as the charge pattern remains undisturbed the picture to be viewed persists.

The flood gun has another use in the operation of direct view storage tubes. An existing charge pattern may be erased from the dielectric surface. To erase the storage surface the potential thereof is varied. This is accomplished by momentarily pulsing the metallic mesh which supports the dielectric to a positive voltage level relative to the flood gun cathode. As a result of capacitive interlock between the metallic mesh and the insulating dielectric, potential level of the latter is increased by a proportional increment. Thus, the dielectric storage surface is brought to potential above the flood gun cathode. Electrons from the flood gun then strike the surface at a velocity insuflicient to produce secondary electron emisice sion. The flood electrons penetrate the dielectric surface and the latter is negatively charged to flood cathode potential at which point flood electrons are repelled. The backing electrode is then returned to the original potential level and the noted capacitive interlock lowers the dielectric surface to its cutoff potential. Erasure of the charge pattern is thus completed.

Desirable flood gun operation, both from the standpoint of display and erasure, requires that the flood electron beam bathe the entire target with electrons of relatively uniform velocity and density per unit area. The desired uniformity has been diflicult to achieve in storage tubes requiring a wide angle beam divergence, for example, tubes having a relatively large viewing surface. In these applications, light output and resolution of the displayed information has proved to be less than desirable. Reducing divergence angle by tube enlargement is, of course, not a satisfactory solution.

Accordingly, it is a primary object of the invention to provide an improved flood gun structure having superior performance characteristics.

It is a further object of the invention to provide a flood gun structure of the type described capable of producing a uniform density flood beam with relatively wide diverging angles and, therefore, adaptable to tubes having a relatively large viewing screen, for example, in excess of seven inches.

It .is a further object of the invention to provide a flood gun of the type described functionally offering improved display resolution and light output.

It is yet another object of the invention to provide a flood gun structure which accomplishes the heretofore noted objectives and is particularly adapted to compact tube construction.

These and other objects and features of the invention will become apparent in the cause of the following description and from the examination of the related drawings, wherein:

FIGURE 1 is a schematic side elevational view of a typical direct view storage tube to which the invention may be applied;

FIG. 2 is a detailed front elevational view of the novel flood gun structure;

FIG. 3 is a sectional view taken along line 3-3 of FIG. 2; and

FIG. 4 is a sectional view modified embodiment of the invention.

Prior to a consideration of the detailed structure of the disclosed invention, attention is directed to FIG. 1 which illustrates a typical direct-view storage tube. The tube comprises an outer evacuated envelope 10 having a viewing screen 12 at the front aspect thereof. The viewing screen 12 comprises a segment of the transparent glass envelope having a layer of phosphor or other luminescent material 14 covering the internal surface thereof.

A storage target is indicated generally at 16 and comprises a metallic mesh backing electrode 17 on the side of the target toward the viewing screen. A storage dielectric 18 is evaporatively positioned on the other surface of mesh 17. A typical dielectric material is zinc sulfide. A collector electrode or mesh 20 is in close juxtaposition with the storage target 16 for the purpose of capturing electrons repelled by the target during operation. Collimator electrode 22 is positioned along the side aspects of the envelope 10 and internally thereof. In operation, the electrode 22 controls the flood beam so that the electrons approach the screen parallel to each other and perpendicular to the screen surface.

At is rear aspect the envelope 10 is necked down as at 24 and has disposed, in the necked down portion, a conventional relatively high velocity electron beam writing gun 26. A deflection yoke 28 controls electron writing similar to FIG. 3 of a slightly beam movement so that the target 16 is scanned in raster fashion during writing or target charging.

As noted above, a flood gun is utilized for the dual purpose of persistent read-out of target stored informa tion and charge erasure from the storage target surface. In FIG. 1, the flood gun is indicated generally and schematically at 30.

Those familiar with storage tube structure will note that a typical flood gun heretofore employed provided a :athode, a first control grid and a second control grid in linear series. The primary function of the first grid is to control beam intensity and shape, while the second grid aids in beam shaping and also induces electron acceleration.

A first embodiment of the invention is shown in FIGS. 2 and 3. The novel flood gun provided comprises an outer annular ring or wall 40 and a substantially parallel inner annular ring or wall 42. A central aperture 44 is defined by :he inner annular ring 42 which extends through the entire structure. The rings 40 and 42 are of uniform axial length as is shown in FIG. 3. A spaced or annular cavity 46 is defined by the walls 40 and 42. The cavity 46 has disposed therein forward bosses 48, 4-8 and rearward bosses 50, 50. The bosses t and 48 serve to capture and mount an upper ceramic disk 52 and a lower ceramic disk 54. The disks 52 and 54, of course, are annular in plane view and substantially fill the cavity 46.

A cathode element 56 is formed with a cross-section configuration of generally inverted U-shape having opposed radially projecting wings 58 and 60 at the terminal aspects of the U-legs. The projections 58 and 60 are captured intermediate the ceramic disks 54 and 52 for element mounting, the upper disk 52 having an annular central opening which allows the U-shaped cathode element to project into annular cavity 46. A typical material employed in the formation of cathode element 56 is barium oxide although other materials may be employed.

The U-shaped cathode element 56 thus is annular as seen in plan view and disposed entirely around and centrally within the cavity 46. As shown in cross-section, the U-shaped cathode element has positioned therein a conventional heating element 62 with appropriate energizing electrical leads 64. Because the heater element 62 is physically disposed within the cathode element 56, heat loss is at a minimum and maximum electron production efficiency results.

In the embodiment of FIGS. 2 and 3, the inner annular wall 42 may have a potential applied thereto and act as a first grid in the operation of the gun. The outer annular wall 40 may also have a potential applied thereto and it acts as one element of a second or accelerating and beam forming grid. Completing the second grid, an openmeshed metallic dome segment 66 covers the entire arrangement and is mounted to the annular wall 40 with clamp 68.

In the operation of the embodiment of FIGS. 2 and 3, the heater 62 is energized, heating cathode element 56 and creating electron emission. By appropriate potential control of the first and second grids, i.e., the wall 42, the wall 40 and the metallic dome 66, the electrons emitted are both accelerated and uniformly diverged to provide an emitted flood beam of uniform intensity as well as density over the entire surface of an engaged storage target.

To illustrate tpyical tube operation of the FIG. 3 embodiment, the inner wall 42 may be held at a potential level within a range of to +10 volts. Consequently, outer wall 40 and dome 60 may be pulsed to a +50 to 150 volt range. Cathode 56 is held at a base or zero voltage and heater 62 within a range of +6.3 to 12 volts. A conductive coating 11 within tube 10 is pulsed to a to +50 volts. Electrode 22, collector electrode 20 and backing electrode 17 have controlled potentials applied thereto in the +50 volt to 80 volt range, the +100 volt to 200 volt range, and the +5 volt to 10 volt range, respectively. With minor variations of the above which may be empirically determined during tube operation an appropriately formed and evenly disposed electron flood beam is achieved.

FIG. 4 illustrates an alternate mode of construction of the novel flood gun. As in the earlier embodiment, an outer annular ring or wall 79 is provided and spaced therefrom an inner annular ring or wall '72. The rings '72 and 70 define therebetween an annular cavity '74. Mounting plates '76 and 73 are connected to the facing surfaces of the rings 70 and 72 and capture therebetween and upper ceramic disk 89 and lower ceramic disk 82. Again, a cathode element 64 is provided of generally U-shape having projections 86 and 38 radially extending from the terminal portions of the U and captured between disks and 82. A heater element 90 is disposed within the cavity defined by the cathode element 84.

In this embodiment annular rings 70 and 72 are electrically connected and act as the accelerating grid. Physically mounted thereon is annular dome 92, of metallic mesh structure. The dome 92 is mounted to the walls 70 and 72 by clamp elements 94, 94. Upstanding walls or plates 96 and 98 are provided which are mounted on the upper disk 80 and embrace the cathode element 84 internally of the Walls 70 and 72.

The operation of this embodiment is substantially similar to that earlier described. Initially, the heater element 90 is energized raising the temperature of the cathode element 84 and inducing electron emis ion. An appropriate potential is applied to metallic walls 96 and 98 which act as a first grid and initially form the emitted electron beam. Walls 70 and 72 and electrically-connected dome 92 may also be energized and act as a secondary grid to cooperate with the first grid to provide beam formation and additionally to accelerate the electron beam toward the target area. Of course, collimating electrodes and the like may be disposed within the envelope 10 to aid in beam formation as is shown in FIG. 1. Typical potential values that may be used in the operation of the embodiment of FIG. 4 are as follows: walls 70, 72 and dome 92, +50 volts to volts; walls 96 and 98, -l() volts to +20 volts; cathode 84, zero volts; and heater 90, +3 volts to 12 volts. Conducting coating 11, electrode 22, collector electrode 20 and backing electrode 17 may be operated as in the previous embodiment of FIG. 3.

It has been found that the gun structure disclosed is particularly useful in storage tubes having a relatively short linear dimension but requiring flood beam of comparatively large diverging angles. The structure is adapted to a gun construction of relatively short axial dimension which contributes to storage tube compactness. The central aperture or opening defined by the inner walls of both embodiments of the gun may be utilized to position a conventional writing gun thereby further conserving space. Alternately, the envelope may be provided with several necked-down portions, one of which could house the writing gun as shown in FIG. 1 and the other of which could house the flood gun. With this configuration either gun may be easily replaced without disturbing the other.

In addition to the above advantages and as compared with prior art flood guns of equivalent power, it has been found that extremely high gain in light output is realized utilizing the structures disclosed.

The invention as shown is by way of illustration and not limitation and may be modified all within the scope of the appended claims.

What is claimed is:

1. In an electron gun,

inner and outer peripheral wall elements defining an open-ended cavity therebetween,

insulating means interconnecting the elements,

an electron producing cathode carried by the insulating means in the cavity and facing said open end, heater means in operative association with the cathode to raise the temperature thereof and induce electron emission and thereby create an electron beam,

and means to form the electron beam into the desired configuration and to accelerate the emitted electrons.

2. An electron gun according to claim 1,

wherein said last-mentioned mean includes a metallic mesh element electrically connected to at least some of said Wall elements.

3. An electron gun according to claim 2,

wherein said forming means comprises first and second grid means,

said first grid means including said inner peripheral wall element,

said second grid means including the outer peripheral wall element, said metallic mesh being carried by and electrically associated with the outer wall element,

and means to apply electrical potentials to the wall elements.

4. An electron gun according to claim 3,

wherein said metallic mesh is dome shaped.

5. An electron gun according to claim 4,

wherein said cavity is annularly continuous,

said cathode forming a continuous ring deposited in the cavity.

6. An electron gun according to claim 5,

wherein said cathode is U-shaped as seen in crosssection,

said heater means being cradled in the cathode element.

'7. An electron gun according to claim 2,

wherein said forming means comprises first and second grid means,

said second grid means comprising said inner and outer peripheral wall elements,

said metallic mesh being carried by and electrically connected with the inner and outer wall elements,

said first grid means comprising plate means disposed within the cavity in operative relation to the cathode element,

and means to apply electrical potentials to the grid means.

8. An electron gun according to claim 7,

wherein said cavity is annularly continuous,

said cathode forming a continuous ring disposed in the cavity,

said plate means being disposed in the cavity and carried by the insulating means on opposed sides of the cathode.

9. An electron gun according to claim 8,

wherein said metallic mesh is dome shaped as seen in elevational view and annularly ring shaped as seen in plan view.

10. An electron gun according to claim 9,

wherein said cathode is U-shaped as seen in crosssection,

said heater means being cradled in the cathode.

References Cited UNITED STATES PATENTS JAMES W. LAWRENCE, Primary Examiner.

V. LAFRANCHI, Assistant Examiner. 

1. IN AN ELECTRON GUN, INNER AND OUTER PERIPHERAL WALL ELEMENTS DEFINING AN OPEN-ENDED CAVITY THEREBETWEEN, INSULATING MEANS INTERCONNECTING THE ELEMENTS, AN ELECTRON PRODUCING CATHODE CARRIED BY THE INSULATING MEANS IN THE CAVITY AND FACING SAID OPEN END, HEATER MEANS IN OPERATIVE ASSOCIATION WITH THE CATHODE TO RAISE THE TEMPERATURE THEREOF AND INDUCE ELECTRON EMISSION AND THEREBY CREATE AND ELECTRON BEAM, AND MEANS TO FORM THE ELECTRON BEAM INTO THE DESIRED CONFIGURATION AND TO ACCELERATE THE EMITTED ELECTRONS. 